Glossary - Global Environmental Issues - page 186

Glossary

Alliance of Small Island States (AOSIS) A group of
states, mainly in the tropics, who consider
themselves most likely to suffer the consequences
of rising sea level and increased storminess expected
to accompany global warming.
anaerobic decay The breakdown of organic material
in the absence of oxygen. Brought about by
anaerobic bacteria, the process commonly causes
the production of methane, a greenhouse gas.
Antarctic ozone hole Intense thinning of the
stratospheric ozone layer above Antarctica, first
reported in the early 1980s by scientists of the
British Antarctic Survey at Halley Bay.
anticyclone A zone of high atmospheric pressure
created by the cooling of air close to the earth's
surface (cold anticyclone) or the sinking of air from
higher levels in the atmosphere (warm anticyclone).
The circulation of air in an anticyclone is clockwise
in the northern hemisphere and counter clockwise
in the southern hemisphere.
aquifer A layer of rock beneath the earth's surface
sufficiently porous and permeable to store
significant quantities of water.
Arctic haze The pollution of the Arctic atmosphere,
mainly in winter, by aerosols such as dust, soot
and sulphate particles originating in Eurasia.
aridity Permanent dryness caused by low average
rainfall, often in combination with high
temperatures.
atmosphere The blanket of air which envelops the solid
earth. It consists of a mixture of gases and aerosols .
atmospheric circulation The large scale movement of
air around and above the earth, associated with
complex but distinct patterns of pressure systems
and wind belts.
atmospheric models Physical or mathematical
representations of the workings of the
atmosphere, ranging from regional models such

A
absorption coefficient A measure of the degree to
which a substance is capable of absorbing radiation.
acid A compound containing hydrogen which on
solution in water produces an excess of hydrogen
ions . An acid reacts with a base or alkali to form a
salt and water.
acid loading The addition of acids to waterbodies by
way of deposition from the atmosphere.
acid precipitation The wet or dry deposition of acidic
substances of anthropogenic origin on the earth's
surface. Commonly called acid rain, but also
includes acid snow and acid fog.
acid rain see acid precipitation and wet deposition .
actual evapotranspiration see evapotranspiration .
actuarial drought forecast An estimation of the
probability of drought based upon past occurrences
in the meteorological record.
Advisory Group on Greenhouse Gases (AGGG) see
Villach Conference .
aerosols Finely divided solid or liquid particles
dispersed in the atmosphere.
Agenda 21 A blueprint for sustainable development
into the twenty-first century produced at the United
Nations Conference on Environment and
Development (UNCED) .
albedo A measure of the reflectivity of the earth's
surface. Newly fallen snow reflects most of the solar
radiation falling on it and has a high albedo; a black
asphalt road surface which readily absorbs
radiation has a low albedo.
algae An order of aquatic plants, occurring in both
fresh and salt water.
alkali A compound which on solution with water
produces an excess of hydroxyl ions (OH).